The present invention relates generally to wireless communication circuits, and in particular to transmit and receive switches.
Unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
One of the more important components in present-day wireless communication equipment is the RF (radio frequency) switch. The purpose of an RF switch is to connect/disconnect an antenna between the transmitter circuitry and the receiver circuitry. Accordingly, such switches are commonly referred to as T/R switches (transmit/receive). T/R designs typically include impedance matching circuitry to direct the high power transmit signal to the antenna while at the same time preventing that signal from entering the sensitive front end of the local receiver (transmit mode), and also allowing a low-loss connection between the antenna and the receiver (receive mode).
For wireless applications (e.g., mobile devices) it is desirable to reduce the size of the RF board and to lower the cost. These two goals can be achieved by fully integrate the T/R switch on-chip; in other words using integrated circuit techniques to form the T/R switch on an integrated circuit (IC) chip. FIG. 6 shows a schematic illustration of a conventional fully integrated on-chip arrangement of a T/R switch circuit based on CMOS (complementary metal-oxide semiconductor) technology.
The IC chip in FIG. 6 includes a power amplifier which can output a transmit signal to be broadcast by an antenna. A low-noise amplifier can accept a receive signal that is sensed by the antenna to be amplified for further processing. The power amplifier and low-noise amplifier can be components which constitutes a transceiver circuit. The circuit arrangement that is between the power amplifier and the low-noise amplifier can be collectively referred to as the T/R switch. The T/R switch includes switch elements (e.g., transistors MT, MRS, and MRP) and impedance matching components (e.g., inductors such as inductor LRS, and capacitors CC, CRS, and CS). The IC chip includes a single tx/rx pin to output the transmit signal for transmission by an antenna and to input a receive signal sensed by the antenna. The switch elements (MT, MRS, and MRP) control whether the transmit signal is output on the tx/rx pin or the signal sensed by the antenna is input via the tx/rx pin. The impedance matching components provide impedance matching between the power amplifier and the antenna, and between the low-noise amplifier and the antenna.
The IC chip is typically assembled on a printed circuit board (PCB), and connected to an “off-chip” component. For example, a balun (balance-unbalance) filter is a typical off-chip component used with the antenna and is assembled on the PCB along with the IC chip. The single tx/rx pin of the IC chip can be connected to the balun filter via a trace formed on the PCB between the tx/rx pin and a pin on the balun filter. Alternatively, the tx/rx pin and balun pin can be connected to respective pads on the PCB, and a bonding wire can be soldered to the pads to make the connection.
The quality factors of on-chip matching components, especially inductors, are usually quite poor due to metal resistance and lossy properties of silicon substrates. Poor quality factors result in limited transmit power and receive sensitivity performance. With on-chip matching components, there is loss of flexibility in fine tuning the RF switch. Since the inductors and capacitors are fabricated on-chip, it is not practical to vary their component values in case fine tuning is needed, for example, to accommodate for impedance variations in the antenna/balun filter assembly. In addition, component values of the on-chip matching elements are subject to process variations and thus may vary from one lot of chips to another. Also, there is loss of flexibility to accommodate different package designs.
These and other issues are addressed by embodiments of the present invention, individually and collectively.